Bacteria on Earth have been found alive as high as 41km. Other living organisms have been found thriving in extreme circumstances, including acidic lakes and hot springs.

NASA probes to Venus have found temperatures in the clouds can be much lower than on the surface. Mysterious dark patches in the clouds absorb light in a similar way to bacteria, previous studies have found.

"Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30-40 percent in the ultraviolet, and muted in longer wavelengths," says Dr Limaye.

"These patches persist for days, changing their shape and contrasts continuously and appear to be scale dependent."